[justtakingpics]

If I have a 50mm f/1.7 lens and I put a bellows on it and move the bellows 50mm. Doesn't that give me 100mm lens? I read somewhere on here that it also means 1:1 magnification. If it does does that mean it is the same a 100mm lens without bellows? I'm confused as to how the bellows makes the lens magnify more and how that differs from a lens without bellows at the same focal length.

to better ask my example, is 50mm + 50mm bellows the same as a 100mm lens? Can I just keep moving the bellows out to get better magnification (where does it top out)? Thanks

[SOldBear]

If I have a 50mm f/1.7 lens and I put a bellows on it and move the bellows 50mm. Doesn't that give me 100mm lens?

No, a 50mm lens + 50mm extension tube or 50mm bellows does not give you a 100mm lens. It gives you a 50mm macro lens.

If it does does that mean it is the same a 100mm lens without bellows? I'm confused as to how the bellows makes the lens magnify more and how that differs from a lens without bellows at the same focal length.

Each lens has a "minimum focusing distance" (MFD). This is the minimum distance from the sensor plane (NOT from the front of the lens) to the object so that the object is still in focus. For most "non-macro" lenses, the MFD is roughly 10X focal length. At this distance, the size of the image on sensor is about 1/8 of the actual size of the object (1:8 magnification ratio).

So a "non-macro" lens with 100mm focal length has MFD about 1m (3 ft).

A lens (or to be exact, the optical part of it) is closest to the sensor plane at infinity focus. To focus closer, the lens has to be moved further from the sensor. You can see this by looking at a single focal (prime) lens: it is shortest at infinity focus, and longest at MFD. A macro lens has the ability to move very far from the sensor. When you add bellows or extension tubes to a "non-macro", you mimic this behavior of a macro lens. You can also add bellows or extension tubes to a macro lens to increase its magnification ratio.

Can I just keep moving the bellows out to get better magnification (where does it top out)?

In theory, yes. In practice, the bellows has limitation as how long it can be. Also, the longer the bellows, the dimmer the viewfinder becomes. And at certain magnification, the stability of the setup (camera, bellows, ....) becomes an issue.

Of course at certain length of the bellows, the object has to be behind the front of the lens to be in focus at the sensor plane! For example, try to add 100mm bellows to a lens with FL of 28mm.

[ytterbium]

To put it simple:

The ultimate limit is when you set the focus 0mm away from the lens front.

This means the lens must be touching the subject for it to be in focus. Or you're photographing dust on the front of lens. If you need to get more magnification at that point, you need longer focal length.

In practice there are other things that would make photography limited in such setting. For example the lens would be so close that not even a ring flash could give good illumination. Photographing a flat surface would be possible only from top, at angle the lens would touch it. And similar problems.

Magnification indicates what is the image size projected on sensor, compared to it's real life size. 1:1, with any lens means, that the lens can focus on subject so close, that it is the same size on sensor, as in real life.
If you know that the APS-C sensor is approx. 15mm in height, imagine a penny over it and you get 1:1 macro.

[mysticcowboy]

In macro photography magnification is written as a ratio. 1:1 means that the actual size of the subject is represented 1 to1 on the sensor or film. 1:3 means that the sensor captures a 1/3 sized image. 3:1 actually magnifies. That captures three times the actual size of the subject. Those numbers are just for illustration. Other magnifications are common.

You can get 1:1 with a 50mm, 100mm (or other) lens. Both will record the same size image. It's just that you will have to get much closer with the 50 to get that magnification.

So lens tubes or bellows will actually increase the magnification of a macro image by allowing a closer focus. They just don't change the focal length.

michael mckee
My Port Townsend – A City in Photographs – 365

[xjx]

To put it simple:

The ultimate limit is when you set the focus 0mm away from the lens front.

.

Not exactly. The distance from the object to the principle plane must be larger than the focal length otherwise there will be no image on the sensor. If the principle plane is located behind the lens front for more than the focal length then your statement is true.

The bellow, however, can theoretically be of any length.

[Blue]

If I have a 50mm f/1.7 lens and I put a bellows on it and move the bellows 50mm. Doesn't that give me 100mm lens? I read somewhere on here that it also means 1:1 magnification. If it does does that mean it is the same a 100mm lens without bellows? I'm confused as to how the bellows makes the lens magnify more and how that differs from a lens without bellows at the same focal length.

to better ask my example, is 50mm + 50mm bellows the same as a 100mm lens? Can I just keep moving the bellows out to get better magnification (where does it top out)? Thanks

Operating under the assumption that the 50mm lens is NOT a macro lens, a 50mm extension tube + your 50mm lens will be ~ a 1:1 macro or "life size" (amt of extension/focal length). If you were to use that same lens with a bellows that could extend out to say about 129mm, you would be at about 2.58:1 or 2.58x life size.

A more precise way to measure magnification requires you to know your lens specs. If you have the lens I think you do, its magnification is rated at 0.15x.

Therefore, Mm = ((ML x FL)+Ex) / FL))

1.15 = ((0.15 x 50) + 50)/50))

Note: ML = mag of your lens = 0.15, FL = focal length of lens = 50, Mm = macro magnification

This method can be used if a macro lens is being used with extension (tubes or bellows or both).
Peter Zack has some info on math associated with various aspects of macro posted here: Shooting Macros Section 3 – The Math | Enticing the Light